Silica-graphenic carbon composite particles and elastomeric materials including such particles

ABSTRACT

Composite particles may be produced by drying slurries containing silica particles and graphenic carbon particles in a liquid carrier. Elastomeric formulations comprising a base elastomer composition and the silica-graphenic carbon composite particles are also disclosed. The formulations possess favorable properties such as increased stiffness and are useful for many applications such as tire treads.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/988,755, filed Aug. 10, 2020, and titled “SILICA-GRAPHENIC CARBONCOMPOSITE PARTICLES AND ELASTOMERIC MATERIALS INCLUDING SUCH PARTICLES”,which in turn claims the benefit of priority of U.S. ProvisionalApplication No. 62/887,856, filed Aug. 16, 2019, and titled“SILICA-GRAPHENIC CARBON COMPOSITE PARTICLES AND ELASTOMERIC MATERIALSINCLUDING SUCH PARTICLES”. All of these applications are incorporated byreference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates to elastomeric materials includingcomposite particles comprising silica and graphenic carbon dispersedtherein.

BACKGROUND OF THE INVENTION

Various fillers have been added to elastomeric compositions. Forexample, carbon black has been utilized in various parts of tiresincluding the tread to reinforce the rubber. In addition, silica hasbeen utilized in tire treads to reinforce the rubber while improvingrolling resistance. While it is desirable to add significant amounts offiller in order to improve certain performance characteristics of tiretread formulations, the large loadings also have detriments inperformance parameters such as viscosity, elongation and hysteresis. Itis of interest to reinforce the rubber and optimize mechanicalproperties without significantly affecting other properties in anegative way.

SUMMARY OF THE INVENTION

An aspect of the present invention provides silica-graphenic carboncomposite particles.

Another aspect of the present invention provides a drying method forproducing silica-graphenic carbon composite particles.

A further aspect of the invention provides reinforced elastomericmaterial comprising a base elastomer composition with silica-grapheniccarbon composite particles dispersed therein.

Another aspect of the invention provides a method of making anelastomeric material comprising mixing dried silica-graphenic carboncomposite particles with a base elastomer composition and curing themixture.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 are SEM images of a silica-graphenic carbon compositeparticle at different magnifications.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

For purposes of this detailed description, it is to be understood thatthe invention may assume various alternative variations and stepsequences, except where expressly specified to the contrary. Moreover,unless otherwise indicated, all numbers expressing quantities used inthe specification and claims are to be understood as being modified inall instances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

The present invention provides silica-graphenic carbon compositeparticles. A slurry or suspension of starting particles of silica andgraphenic carbon in a liquid carrier may be provided, which is dried toform a powder comprising silica-graphenic carbon composite particles.For example, each composite particle may comprise a combination ofsilica particles and graphenic carbon nanosheets in which the silicaparticles contact each other to form a continuous or interconnectednetwork of silica particles, and the graphenic carbon nanosheets aredistributed throughout the composite particle. Each composite particlemay thus comprise multiple silica particles and multiple grapheniccarbon nanosheets adhered or agglomerated to form the compositeparticle. In such agglomerated composite particles, the silica particlesand graphenic carbon nanosheets may be uniformly distributed throughouteach particle, or non-uniformly distributed. The surface of eachcomposite particle typically comprises silica particles and may includegraphenic carbon particles on a limited portion of the surface, ratherthan having a surface entirely of graphenic carbon particles. Forexample, the graphenic carbon particles may be provided in the form ofgraphene nanosheets that cover less than 50 percent of the surface areaof each composite particle, for example, less than 25 percent, or lessthan 10 percent.

The silica-graphenic carbon composite particles may be combined with anelastomeric material to provide a continuous matrix of the elastomericmaterial with the composite particles dispersed therein. Such reinforcedelastomeric materials may exhibit improved properties due to thedispersed silica-graphenic carbon composite particles, for example,improved mechanical properties including increased stiffness,elongation, combined elongation and hardness, abrasion resistance, wearresistance, tear strength, hysteresis and the like.

At least a portion of the silica-graphenic carbon composite particlesmay be comminuted to provide smaller particles before or duringintroduction into the elastomeric material, e.g., the dried compositeparticles may be broken up into smaller composite particles.Alternatively, the composite particles may be compacted, consolidated orotherwise combined into larger granules comprising multiplesilica-graphenic carbon composite particles prior to introduction intothe elastomeric material.

The silica-graphenic carbon composite particles may typically comprisefrom 60 to 99.9 weight percent silica and from 0.1 to 40 weight percentgraphenic carbon particles, for example, from 70 to 99.8 weight percentsilica and from 0.2 to 30 weight percent graphenic carbon particles, orfrom 75 to 99.7 weight percent silica and from 0.3 to 25 weight percentgraphenic carbon particles, or from 80 to 99.6 weight percent silica andfrom 0.4 to 20 weight percent graphenic carbon particles.

The composite silica-graphenic carbon composite particles may typicallyhave an average particle size of from 1 to 500 microns, for example,from 2 to 100 microns, or from 3 to 10 microns, as measured using FieldEmission Scanning Electron Microscopy (FE-SEM).

The silica-graphenic carbon composite particles may have an averagesurface area of from 50 to 1,000 square meters per gram, for example,from 70 to 230 square meters per gram, or from 90 to 200 square metersper gram, or from 150 to 170 square meters per gram as measured by thestandard CTAB method according to the ASTM D6845 test.

The silica-graphenic carbon composite particles may be present in theelastomeric materials in typical amounts of from 5 to 70 weight percentor from 10 to 60 weight percent or from 20 to 60 weight percent, forexample, from 30 to 50 weight percent. It is desirable to control theamount of composite particles present in the formulation in order toimprove traction and stiffness when the elastomeric material is used intire treads, e.g., it may be desirable to add the composite particles inamounts greater than 5 or 10 weight percent, for example, greater than20 or 30 weight percent.

The relative amounts of silica and graphenic carbon contained in thecomposite particles are controlled such that the amount of grapheniccarbon may be optimized to an amount that provides desirable propertiessuch as improvements in stiffness. For example, for improved stiffnessproperties of elastomeric materials, the amount of silica in thecomposite particles may be greater than 70 weight percent, or greaterthan 90 weight percent, while the amount of graphenic carbon particlesmay be less than 30 weight percent, such as less than 10 weight percent,such as less than 8 weight percent, or such as 6 weight percent, basedupon the weight of the composite particles.

Such composite silica/graphenic carbon particles may be dispersed in anelastomeric composition. Elastomeric formulations in accordance with thepresent invention may be useful in various applications including tirecomponents such as vehicle tire treads, subtreads, tire carcasses, tiresidewalls, tire belt wedge, tire beads, and tire wire skim coats, wiresand cable jacketing, hoses, gaskets and seals, industrial and automotivedrive-belts, engine mounts, V-belts, conveyor belts, roller coatings,shoe sole materials, packing rings, damping elements, and the like.While tire tread formulations are described herein as a particularembodiment of the invention, it is to be understood that the elastomericformulations of the present invention are not limited to such uses andmay be used in various other applications.

The elastomeric formulations of the present invention comprise a baseelastomeric composition to which silica-graphenic carbon compositeparticles are added. The elastomeric formulations may comprise syntheticrubber, natural rubber, mixes thereof and the like. For example, theelastomeric composition may comprise styrene butadiene co-polymer,polybutadiene, halobutyl and/or natural rubber (polyisoprenes). For usein tire treads, the base elastomeric composition typically comprisesfrom 30 to 70 weight percent of the overall tire tread formulation, forexample from 40 to 55 weight percent.

The elastomeric formulation may comprise a curable rubber. As usedherein, the term “curable rubber” means both natural rubber and itsvarious raw and reclaimed forms as well as various synthetic rubbers.For example, the curable rubber can include styrene/butadiene rubber(SBR), butadiene rubber (BR), butyl rubber, ethylene propylene dienemonomer (EPDM) rubber, nitrile rubber, chloroprene rubber, siliconerubber, fluoroelastomer rubber, natural rubber, any other known type oforganic rubber, and combinations thereof. As used herein, the terms“elastomer”, “rubber” and “rubbery elastomer” can be usedinterchangeably, unless indicated otherwise. The terms “rubbercomposition”, “compounded rubber” and “rubber compound” can be usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials, and such terms are well-known tothose having skill in the rubber mixing or rubber compounding art.

As described more fully below, the composite silica and graphenic carbonparticles may be produced from individual particles of silica andgraphenic carbon that are mixed together in a liquid carrier and dried.The silica starting particles used to make the composite silica andgraphenic carbon particles may include precipitated silica, colloidalsilica, silica gel, and mixtures thereof. The starting silica particlescan have an average particle size of less than 200 microns, or from 1 to50 microns, or from 5 to 20 microns, as measured by electron microscope.The starting silica particles can have a typical surface area of from 25to 1,000 or from 75 to 350 or from 80 to 250 square meters per gram. Thesurface area can be measured using conventional techniques known in theart. As used herein, the surface area is determined by the Brunauer,Emmett, and Teller (BET) method according to ASTM D1993-91. The BETsurface area can be determined by fitting five relative-pressure pointsfrom a nitrogen sorption isotherm measurement made with a MicromeriticsTriStar 3000™ instrument. A FlowPrep-060™ station provides heat and acontinuous gas flow to prepare samples for analysis. Prior to nitrogensorption, the silica samples are dried by heating to a temperature of160° C. in flowing nitrogen (P5 grade) for at least one (1) hour.

The silica particles for use in the present invention can be preparedusing a variety of methods known to those having ordinary skill in theart, such as colloidal silica, precipitated silica, fumed silica, silicagels and the like. For example, the silica may be produced by themethods disclosed in U.S. patent application Ser. No. 11/103,123, whichis incorporated herein by reference. For example, silica for use asuntreated filler can be prepared by combining an aqueous solution ofsoluble metal silicate with acid to form a silica slurry. The silicaslurry can be optionally aged, and acid or base can be added to theoptional aged silica slurry. The silica slurry can be filtered,optionally washed, and optionally dried using conventional techniquesknown to a skilled artisan.

The silica may further comprise various surface treatments such as, butnot limited to, those described in U.S. Pat. No. 3,873,489 at column 5line 45 to column 6 line 56. Such surface treatments may be providedprior to, during, or after combination with the graphenic carbonparticles. For example, such surface treatments may be provided on thedried silica-graphenic carbon composite particles.

The starting graphenic carbon particles used to produce thesilica-graphenic carbon composite particles may have certain desirablecharacteristics. As used herein, the term “graphenic carbon particles”means carbon particles having structures comprising one or more layersof one-atom-thick planar sheets of sp² or sp³ bonded carbon atoms.

In certain embodiments, the graphenic carbon particles may comprisegraphite oxide, wherein the graphite oxide has a carbon to oxygen atomicratio ranging from 2:1 to 25:1. Graphite oxide can be prepared, forexample, by oxidation of graphite with potassium chlorate in a graphiteand nitric acid mixture, or using other oxidizers.

In certain embodiments, the graphenic carbon particles may comprisegraphene oxide (GO). GO is chemically similar to graphite oxide butinstead of having a multi-layer structural arrangement, it comprisesexfoliated monolayers of few-layered stacks. GO can be prepared bythermal exfoliation of graphite oxide as described in U.S. Pat. No.7,658,901. The graphene oxide can also be prepared, for example, bydispersing in water, micro-mechanical exfoliation, chemical vapordeposition or chemical exfoliation of graphite oxide. Graphene oxidesuitable for the present invention may have a thickness from 1 nm to1,500 nm and average width ranging from 10 to 100 microns.

The graphene oxide used to produce the silica-graphenic carbon compositeparticles may be obtained from commercial sources, for example, grapheneoxide powder or graphene oxide water suspension from Graphenea and othercommercial sources. Such commercially available graphene oxide materialsmay be produced by known techniques in which layer(s) of graphite oxideare exfoliated to provide thin sheets.

In another embodiment, the graphenic carbon particles may consist ofreduced graphene oxide (rGO). Reduced graphene oxide can be obtained bychemical reduction, thermal reduction, or UV light reduction of grapheneoxide. Reduced graphene oxide resembles graphene but may containresidual oxygen and other heteroatoms, as well as structural defects.

The reduced graphene oxide used to produce the silica-graphenic carboncomposite particles may be obtained from commercial sources, forexample, reduced graphene oxide powder from Graphenea and othercommercial sources.

For example, the synthesis of reduced rGO nanoparticles may be preparedas described in U.S. Pat. No. 9,815,701.

In certain embodiments, graphenic carbon particles include graphene,composed of structures comprising one or more layers of one-atom-thickplanar sheets of sp² bonded carbon atoms that are densely packed in ahoneycomb crystal lattice. The average number of stacked layers may beless than 100, for example, less than 50. In certain embodiments, theaverage number of stacked layers is 30 or less, such as 20 or less, 10or less, or, in some cases, 5 or less. The graphenic carbon particlesmay be substantially flat, however, at least a portion of the planarsheets may be substantially curved, curled, creased or buckled. Theparticles typically do not have a spheroidal or equiaxed morphology. Thegraphenic carbon particles may be in the form of graphene nanosheets.

The graphenic carbon particles used to produce the silica-grapheniccarbon composite particles of the present invention may have athickness, measured in a direction perpendicular to the carbon atomlayers, of no more than 10 nanometers, or no more than 5 nanometers, orno more than 4 or 3 or 2 or 1 nanometers, such as no more than 3.6nanometers. The graphenic carbon particles may be from 1 atom layer upto 3, 6, 9, 12, 20 or 30 atom layers thick, or more. The grapheniccarbon particles may have a width and length, measured in a directionparallel to the carbon atoms layers, of at least 20 nanometers, at least50 nanometers, or at least 100 nanometers. The graphenic carbonparticles may have a width and length of up to 200 nanometers or up to500 nanometers. The graphenic carbon particles may have a width andlength in the range of from 20 to 500 nanometers, such as 20 to 200nanometers, such as 50 to 500 nanometers, such as 100 to 500 nanometers,or from 100 to 200 nanometers. The graphenic carbon particles may beprovided in the form of ultrathin flakes, platelets or sheets havingrelatively high aspect ratios (aspect ratio being defined as the ratioof the longest dimension of a particle to the shortest dimension of theparticle) of greater than 3:1, such as greater than 10:1.

The graphenic carbon particles used to produce the silica-grapheniccarbon composite particles of the present invention have relatively lowoxygen content. For example, the graphenic carbon particles may, evenwhen having a thickness of no more than 5 or no more than 2 nanometers,have a carbon to oxygen atomic ratio greater than 25:1. The oxygencontent of the graphenic carbon particles can be determined using X-rayPhotoelectron Spectroscopy, such as is described in D. R. Dreyer et al.,Chem. Soc. Rev. 39, 228-240 (2010).

The graphenic carbon particles may typically have a B.E.T. specificsurface area of at least 50 square meters per gram, such as 70 to 1,000square meters per gram, or, in some cases, 200 to 1,000 square metersper grams or 200 to 400 square meters per gram. As used herein, the term“B.E.T. specific surface area” refers to a specific surface areadetermined by nitrogen adsorption according to the ASTMD 3663-78standard based on the Brunauer-Emmett-Teller method described in theperiodical “The Journal of the American Chemical Society”, 60, 309(1938).

The graphenic carbon particles used to produce the silica-grapheniccarbon composite particles of the present invention may have a Ramanspectroscopy 2D/G peak ratio of at least 0.8:1, for example, at least1.05:1, or at least 1.1:1, or at least 1.2:1 or at least 1.3:1. As usedherein, the term “2D/G peak ratio” refers to the ratio of the intensityof the 2D peak at 2692 cm⁻¹ to the intensity of the G peak at 1,580cm⁻¹.

The graphenic carbon particles may have a relatively low bulk density.For example, the graphenic carbon particles may be characterized byhaving a bulk density (tap density) of less than 0.2 g/cm³, such as nomore than 0.1 g/cm³. For the purposes of the present invention, the bulkdensity of the graphenic carbon particles is determined by placing 0.4grams of the graphenic carbon particles in a glass measuring cylinderhaving a readable scale. The cylinder is raised approximately one inchand tapped 100 times, by striking the base of the cylinder onto a hardsurface, to allow the graphenic carbon particles to settle within thecylinder. The volume of the particles is then measured, and the bulkdensity is calculated by dividing 0.4 grams by the measured volume,wherein the bulk density is expressed in terms of g/cm³.

The graphenic carbon particles may have a compressed density and apercent densification that is less than the compressed density andpercent densification of graphite powder and certain types ofsubstantially flat graphenic carbon particles. Lower compressed densityand lower percent densification are each currently believed tocontribute to better dispersion and/or rheological properties thangraphenic carbon particles exhibiting higher compressed density andhigher percent densification. The compressed density of the grapheniccarbon particles may be 0.9 g/cm³ or less, such as less than 0.8 g/cm³,such as less than 0.7 g/cm³, such as from 0.6 to 0.7 g/cm³. The percentdensification of the graphenic carbon particles is less than 40%, suchas less than 30%, such as from 25 to 30%.

For purposes of the present invention, the compressed density ofgraphenic carbon particles is calculated from a measured thickness of agiven mass of the particles after compression. Specifically, themeasured thickness is determined by subjecting 0.1 grams of thegraphenic carbon particles to cold press under 15,000 pounds of force ina 1.3-centimeter die for 45 minutes, wherein the contact pressure is 500MPa. The compressed density of the graphenic carbon particles is thencalculated from this measured thickness according to the followingequation:

${{Compressed}{Density}\left( {g/{cm}^{3}} \right)} = \frac{0.1{grams}}{\Pi*\left( {1.3{cm}/2} \right)^{2}*\left( {{measured}{thickness}{in}{cm}} \right)}$

The percent densification of the graphenic carbon particles is thendetermined as the ratio of the calculated compressed density of thegraphenic carbon particles, as determined above, to 2.2 g/cm³, which isthe density of graphite.

The graphenic carbon particles may have a measured bulk liquidconductivity of at least 100 microSiemens, such as at least 120microSiemens, such as at least 140 microSiemens immediately after mixingand at later points in time, such as at 10 minutes, or 20 minutes, or 30minutes, or 40 minutes. For the purposes of the present invention, thebulk liquid conductivity of the graphenic carbon particles is determinedas follows. First, a sample comprising a 0.5% solution of grapheniccarbon particles in butyl cellosolve is sonicated for 30 minutes with abath sonicator. Immediately following sonication, the sample is placedin a standard calibrated electrolytic conductivity cell (K=1). A FisherScientific AB 30 conductivity meter is introduced to the sample tomeasure the conductivity of the sample. The conductivity is plotted overthe course of about 40 minutes.

The graphenic carbon particles used to produce the silica-grapheniccarbon composite particles may be obtained from commercial sources, forexample, exfoliated graphene from Angstron, XG Sciences and othercommercial sources. Such commercially available graphene particles maybe produced by known exfoliation techniques in which layer(s) ofgraphene are removed from graphite substrates to provide thin graphenesheets.

The graphenic carbon particles may be thermally produced in accordancewith the methods and apparatus described in U.S. Pat. Nos. 8,486,363,8,486,364 and 9,221,688, which are incorporated herein by reference.Such thermally produced graphenic carbon particles are commerciallyavailable from Raymor NanoIntegris under the designation PureWave.

The graphenic carbon starting particles can be made, for example, bythermal processes. The graphenic carbon particles may be produced fromcarbon-containing precursor materials that are heated to hightemperatures in a thermal zone. For example, the graphenic carbonparticles may be produced by the systems and methods disclosed in U.S.Pat. Nos. 8,486,363, 8,486,364 and 9,221,688, which are incorporatedherein by reference.

The graphenic carbon particles may be made by using the apparatus andmethod described in U.S. Pat. No. 8,486,363, in which (i) one or morehydrocarbon precursor materials capable of forming a two-carbon fragmentspecies (such as n-propanol, ethane, ethylene, acetylene, vinylchloride, 1,2-dichloroethane, allyl alcohol, propionaldehyde, and/orvinyl bromide) is introduced into a thermal zone (such as a plasma); and(ii) the hydrocarbon is heated in the thermal zone to a temperature ofat least 1,000° C. to form the graphenic carbon particles. The grapheniccarbon particles may be made by using the apparatus and method describedin U.S. Pat. No. 8,486,364, in which (i) a methane precursor material(such as a material comprising at least 50 percent methane, or, in somecases, gaseous or liquid methane of at least 95 or 99 percent purity orhigher) is introduced into a thermal zone (such as a plasma); and (ii)the methane precursor is heated in the thermal zone to form thegraphenic carbon particles. Such methods can produce graphenic carbonparticles having at least some, in some cases all, of thecharacteristics described above.

During production of the graphenic carbon particles by the methodsdescribed above, a carbon-containing precursor is provided as a feedmaterial that may be contacted with an inert carrier gas. Thecarbon-containing precursor material may be heated in a thermal zone,for example, by a plasma system. The precursor material may be heated toa temperature ranging from 1,000° C. to 20,000° C., such as 3,500° C. to20,000° C., or 1,200° C. to 10,000° C. For example, the temperature ofthe thermal zone may range from 1,500° C. to 8,000° C., such as from2,000° C. to 5,000° C. Although the thermal zone may be generated by aplasma system, it is to be understood that any other suitable heatingsystem may be used to create the thermal zone, such as various types offurnaces including electrically heated tube furnaces and the like.

Without being bound by any theory, it is currently believed that theforegoing thermal methods of manufacturing graphenic carbon particlesare particularly suitable for producing graphenic carbon particleshaving relatively low thickness and relatively high aspect ratio incombination with relatively low oxygen content, as described above.Moreover, such methods are currently believed to produce a substantialamount of graphenic carbon particles having a substantially curved,curled, creased or buckled morphology (referred to herein as a “3D”morphology), as opposed to producing predominantly particles having asubstantially two-dimensional (or flat) morphology.

In accordance with certain aspects of the present invention, dryingmethods, such as spray drying, are used to produce the silica-grapheniccarbon composite particles. The starting silica particles and grapheniccarbon particles may be dispersed into liquid carriers to form slurries,followed by drying to produce the composite particles. For example, drysilica powders may be formed into slurries, followed by addition of thegraphenic carbon particles, or dry silica powders may be added to aslurry comprising the graphenic carbon particles. Alternatively, thegraphenic carbon particles may be combined with a silica slurry in situ,e.g., without first drying the silica.

The silica-graphenic carbon composite particles may be made by in situtechniques, e.g., in which the silica particles are formed in a slurryto which the graphenic carbon particles are added, the silica particlesare precipitated in the presence of graphenic carbon particles and/orthe graphenic carbon particles are added during or after precipitationof the silica. The combination of silica particles and graphenic carbonparticles may be formed in situ and may be subjected to drying toproduce the silica-graphenic carbon composite particles without priordrying of the silica particles.

Suitable liquid carriers for use in the slurries include water and/ororganic solvents such as ethanol, methanol, acetone, chloroform,dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethyl acetate,glycerin, methylene chloride, tetrahydrofuran (THF), and the like. Theliquid carrier may be present in a typical amount of from 55 to 95weight percent based on the total weight of the dispersion, for example,from 70 to 90 weight percent, or from 75 to 85 weight percent.

In addition to a liquid carrier, the dispersions may include adispersing agent. Suitable dispersing agents include polymericdispersants such as polyvinylpyrrolidone (PVP), acrylics, amines, epoxyand the like. Such dispersing agents may be present in the water orother solvent in a typical amount of from 0 to 50 weight percent basedon the total weight of the solvent and dispersant, for example, from 1to 30 weight percent, or from 2 to 20 weight percent.

Other additives may optionally be included in the dispersions, such asdefoamers, surfactants, rheology modifiers and UV absorbers.

A typical dispersion may contain from 0.01 to 80 weight percent silicaparticles based on the total weight of the dispersion, for example, from10 to 25 weight percent.

A typical dispersion may contain from 0.01 to 30 weight percentgraphenic carbon particles based on the total weight of the dispersion,for example, from 0.1 to 10 weight percent.

The total combined amount of silica particles and graphenic carbonparticles of such dispersions may typically comprise from 0.01 to 50weight percent, for example, from 1 to 35 weight percent, or from 10 to25 weight percent based on the total weight of the dispersion.

When a dispersant such as PVP is included in the dispersion, it may bepresent in a typical amount of from 0.1 to 10 weight percent based uponthe total combined amount of dispersant, silica and graphenic carbon(excluding the solvent), for example, from 0.5 to 5 weight percent, orfrom 1 to 3 weight percent.

Separate dispersions of silica particles and graphenic carbon particlesmay be made, followed by combining the dispersions prior to drying. Forexample, the graphenic carbon particles may be dispersed in awater/polymeric dispersant liquid as described above, while the silicaparticles may be dispersed in water alone, or a combination of water anddispersant such as polyvinylpyrrolidone (PVP), acrylics, amine, epoxy orthe like.

The composite particles may be dried using conventional dryingtechniques. Non-limiting examples of such techniques include ovendrying, vacuum oven drying, rotary dryers, spray drying or spin flashdrying. Non-limiting examples of spray dryers include rotary atomizersand nozzle spray dryers. Spray drying can be carried out using anysuitable type of atomizer, in particular a turbine, nozzle,liquid-pressure or twin-fluid atomizer. The washed silica solids may notbe in a condition that is suitable for spray drying. For example, thewashed composite solids may be too thick to be spray dried. In oneaspect of the above-described process, the washed composite solids,e.g., the washed filter cake, are mixed with water to form a liquidsuspension and the pH of the suspension adjusted, if required, withdilute acid or dilute alkali, e.g., sodium hydroxide, to a pH value inthe range from 6 to 7, e.g., 6.5, and then fed to the inlet nozzle ofthe spray dryer.

The temperature at which the composite particles are dried can varywidely but will be below the fusion temperature of the composite.Typically, the drying temperature will be above room temperature and mayrange from above 50° C. to less than 900° C., e.g., from above 100° C.,e.g., 200° C., to 500° C. In one aspect of the above-described process,the composite solids are dried in a spray dryer having an inlettemperature of approximately 500° C. and an outlet temperature ofapproximately 105° C. The free water content of the dried composite canvary but may typically be in the range of from approximately 1 to 10weight percent e.g., from 4 to 7 weight percent. As used herein, theterm free water means water that can be removed from the composite byheating it for 24 hours at from 100° C. to 200° C., e.g., 105° C.

The pressure at which the composite particles can be dried can varywidely, for example, at atmospheric pressure, or under vacuum.

In one aspect of the process described herein, the dried composite isforwarded directly to a granulator where it is compacted and granulatedto obtain a granular product. Dried composite can also be subjected toconventional size reduction techniques, e.g., as exemplified by grindingand pulverizing. Fluid energy milling using air or superheated steam asthe working fluid can also be used. The precipitated composite obtainedmay usually be in the form of a powder. The composite product exitingthe granulator can have a wide distribution of particle sizes, e.g.,between −5 and +325 Mesh. If subjected to a size reduction operation,the composite product can be subjected to a sizing operation, e.g.,separated into conforming and non-conforming size materials by means,for example, of vibrating screens with appropriate mesh sizes.Non-conforming product can be recycled to the size reduction orcompaction processes. The sized composite product can be separated intoa product having size range of between −18 and +230 Mesh, e.g., between−60 and +100 Mesh. Mesh sizes are in accordance with ASTM E11 ASD.

The elastomeric materials of the present invention may be made bycombining the composite silica and graphenic carbon particles withemulsion and/or solution polymers as described above, e.g., organicrubber comprising solution styrene/butadiene (SBR), polybutadiene rubberor a mixture thereof, to form a master batch. Curable rubbers for use inthe master batch can vary widely and are well known to the skilledartisan and can include vulcanizable and sulfur-curable rubbers. Forexample, curable rubbers can include those used for mechanical rubbergoods and tires. A non-limiting example of a master batch can comprise acombination of organic rubber, water-immiscible solvent, treated fillerand, optionally, processing oil. Such a product can be supplied by arubber producer to a tire manufacturer. A benefit to a tire manufacturerusing a master batch can be that the composite silica and grapheniccarbon particles are substantially uniformly dispersed in the rubber,which can result in substantially reducing or minimizing the mixing timeto produce the compounded rubber. In a non-limiting example, the masterbatch can contain from 10 to 150 parts of composite particles per 100parts of rubber (phr).

The composite silica and graphenic carbon particles can be mixed with anuncured rubbery elastomer used to prepare the vulcanizable rubbercomposition by conventional means such as in a Banbury mixer or on arubber mill at temperatures from 100° F. to 392° F. (38° C.-200° C.).Non-limiting examples of other conventional rubber additives present inthe rubber composition can include conventional sulfur or peroxide curesystems. In alternate non-limiting examples, the sulfur-cure system caninclude from 0.5 to 5 parts sulfur, from 2 to 5 parts zinc oxide, andfrom 0.5 to 5 parts accelerator. In further alternate non-limitingexamples, the peroxide-cure system can include from 1 to 4 parts of aperoxide such as dicumyl peroxide.

In addition to the silica-graphenic carbon composite particles in theamounts described above, the elastomeric formulations may also comprisefillers. Suitable additional fillers for use in the rubber formulationsof the present invention can include a wide variety of materials knownto one having ordinary skill in the art such as, for example, clays,talc, carbon black, and the like. Non-limiting examples can includeinorganic oxides such as but not limited to inorganic particulate oramorphous solid materials which possess either oxygen (chemisorbed orcovalently bonded) or hydroxyl (bound or free) at an exposed surfacesuch as but not limited to oxides of the metals in Periods 2, 3, 4, 5and 6 of Groups Ib, IIb, IIIa, IIIb, IVa, IVb (except carbon), Va, VIa,VIIa and VIII of the Periodic Table of the Elements in AdvancedInorganic Chemistry: A Comprehensive Text by F. Albert Cotton et al.,Fourth Edition, John Wiley and Sons, 1980. Non-limiting examples ofinorganic oxides for use in the present invention can include aluminumsilicates, alumina, and mixtures thereof. Suitable metal silicates caninclude a wide variety of materials known in the art. Non-limitingexamples can include but are not limited to alumina, lithium, sodium,potassium silicate, and mixtures thereof.

Non-limiting examples of conventional rubber additives can includeprocessing oils, plasticizers, accelerators, retarders, antioxidants,curatives, metal oxides, heat stabilizers, light stabilizers, ozonestabilizers, organic acids, such as for example stearic acid, benzoicacid, or salicylic acid, other activators, extenders and coloringpigments. The compounding recipe selected will vary with the particularvulcanizate prepared. Such recipes are well known to those skilled inthe rubber compounding art. In a non-limiting example, a benefit of theuse of silica-graphenic carbon composite particles of the presentinvention when the coupling material is mercaptoorganometalliccompound(s) can be the stability at elevated temperatures of a rubbercompound containing such composite particles, and essentially theabsence of curing of a rubber compounded therewith at temperatures up toat least 200° C. when mixed for at least one-half minute or up to 60minutes.

In alternate non-limiting examples, the compounding process can beperformed batch-wise or continuously. In a further non-limiting example,the rubber composition and at least a portion of the composite silicaand graphenic carbon particles can be continuously fed into an initialportion of a mixing path to produce a blend and the blend can becontinuously fed into a second portion of the mixing path.

The addition of silica-graphenic carbon composite particles toelastomeric materials in accordance with aspects of the presentinvention may produce improved mechanical properties such as stiffness,elongation, combined elongation and hardness, abrasion resistance, wearresistance and the like. For example, stiffness of the reinforcedelastomeric materials may be increased in comparison to unreinforcedelastomeric material or in comparison to an elastomeric materialcontaining conventional particles such as silica particles dispersedtherein, or to an elastomeric material containing silica particlesdispersed therein and graphenic carbon particles dispersed in theelastomer, but added separately and not as part of the silica-grapheniccarbon composite. For example, a silica-graphenic carbon compositeparticle-reinforced elastomeric material of the present invention mayhave a stiffness that is at least 5 percent or 10 percent or 20 percentgreater than the same elastomeric material containing the same amount ofsilica particles having the same average particle size as thesilica-graphenic carbon composite particles of the present invention.

The quality of silica dispersion and graphenic carbon dispersion inrubber may be determined using a piece of equipment called aDisperGrader (commercially available from Alpha Technologies). Whenexamining rubber samples using this device, the amount of white areashould be at a minimum. The dispersion of composite silica and graphenicparticles may be important for consistent performance, wear, obtaininggood reinforcement, and for limiting failures such as crack propagation.Thus, fillers that significantly reduce composite particle dispersionmay not be acceptable.

Silica-graphenic carbon composite particles, a method of makingsilica-graphenic carbon composite particles, an elastomeric formulation,and a method of making an elastomeric formulation may be characterizedby one or more of the following aspects.

In a first aspect, the present invention may relate to silica-grapheniccarbon composite particles comprising from 60 to 99.9 weight percentsilica, and from 0.1 to 40 weight percent graphenic carbon.

In a second aspect, the silica-graphenic carbon composite particles inaccordance with the first aspect have an average particle size of from 1to 500 microns, such as from 2 to 100 microns, or from 3 to 10 microns,as determined using FE-SEM.

In a third aspect, the graphenic carbon in accordance with the firstaspect or the second aspect is in the form of graphene nanosheets.

In a fourth aspect, the graphene nanosheets in accordance with the thirdaspect have an average thickness of less than 10 nanometers.

In a fifth aspect, the graphene nanosheets in accordance with the thirdaspect or fourth aspect have average widths and lengths of from 20 to200 nanometers.

In a sixth aspect, the graphenic carbon in accordance with the firstaspect or the second aspect is selected from graphite oxide, grapheneoxide, rGO, and combinations thereof.

In a seventh aspect, the graphenic carbon in accordance with any one ofthe first to sixth aspects is dispersed throughout each compositeparticle.

In an eighth aspect, the silica in accordance with any one of the firstto seventh aspects comprises a continuous or interconnected network inwhich the graphenic carbon is dispersed.

In a ninth aspect, the surface of each composite particle in accordancewith any one of the first to eighth aspects comprises the silica.

In a tenth aspect, a portion of the surface of each composite particlein accordance with any one of the first to ninth aspects comprises thegraphenic carbon.

In an eleventh aspect, less than 50 percent, such as less than 25percent, or less than 10 percent of the surface area of each compositeparticle in accordance with any one of the first to tenth aspectscomprises the graphenic carbon.

In a twelfth aspect, the silica-graphenic carbon composite particles inaccordance with any one of the first to eleventh aspects comprise from70 to 99.8 weight percent silica and from 0.2 to 30 weight percentgraphenic carbon, or from 75 to 99.7 weight percent silica and from 0.3to 25 weight percent graphenic carbon, or from 80 to 99.6 weight percentsilica and from 0.4 to 20 weight percent graphenic carbon.

In a thirteenth aspect, the present invention may relate to a method ofmaking silica-graphenic carbon composite particles, the methodcomprising drying a slurry comprising silica particles, graphenic carbonparticles, and a liquid carrier to thereby produce the silica-grapheniccarbon composite particles, such as the silica-graphenic carboncomposite particles of any one of the first through twelfth aspects.

In a fourteenth aspect, the drying according to the thirteenth aspectcomprises spray drying.

In a fifteenth aspect, the liquid carrier according to the thirteenthaspect or fourteenth aspect comprises water.

In a sixteenth aspect, the slurry according to any one of the thirteenthto fifteenth aspects comprises a dispersing agent.

In a seventeenth aspect, the slurry according to any one of thethirteenth to sixteenth aspects is prepared by making separatedispersions of silica particles and graphenic particles, followed bycombining the dispersions prior to drying.

In an eighteenth aspect, the slurry according to any one of thethirteenth to sixteenth aspects is prepared by forming dry silicapowders into slurries, followed by addition of the graphenic carbonparticles, or by adding dry silica to a slurry comprising the grapheniccarbon particles.

In a nineteenth aspect, the present invention may relate to anelastomeric formulation comprising a base elastomer composition and from5 to 70 weight percent silica-graphenic carbon composite particles.

In a twentieth aspect, the elastomeric formulation in accordance withthe nineteenth aspect comprises natural rubber, synthetic rubber, orcombinations thereof.

In a twenty-first aspect, the elastomeric formulation in accordance withthe nineteenth aspect or the twentieth aspect comprisesstyrene/butadiene rubber, butadiene rubber, butyl rubber, EPDM rubber,nitrile rubber, chloroprene rubber, silicone rubber, fluoroelastomerrubber, natural rubber and/or functionalized derivatives thereof.

In a twenty-second aspect, the elastomeric formulation in accordancewith any one of the nineteenth to twenty-first aspects comprises a tiretread formulation.

In a twenty-third aspect, the elastomeric formulation in accordance withany one of the nineteenth to twenty-second aspects comprises at leastone additive selected from processing oils, antioxidants, curatives, andmetal oxides.

In a twenty-fourth aspect, the silica-graphenic carbon compositeparticles in accordance with any one of the nineteenth to twenty-thirdaspects comprise from 30 to 50 weight percent of the formulation.

In a twenty-fifth aspect, the elastomeric formulation in accordance withany one of the nineteenth to twenty-fourth aspects comprises from 10 to150 parts of composite particles per 100 parts of rubber.

In a twenty-sixth aspect, the present invention may relate to a methodof making an elastomeric formulation comprising mixing silica-grapheniccarbon composite particles with a base elastomer composition and curingthe mixture.

In a twenty-seventh aspect, the base elastomer composition in accordancewith the method of the twenty-sixth aspect comprises an organic rubber.

In a twenty-eighth aspect, the mixing step of the method in accordancewith the twenty-sixth aspect or the twenty-seventh aspect furthercomprises mixing the composite particles and the base elastomercomposition with a water-immiscible solvent, a filler, and, optionally,a processing oil.

In a twenty-ninth aspect, the mixing step of the method in accordancewith any one of the twenty-sixth to twenty-eighth aspects furthercomprises mixing the composite particles and the base elastomercomposition with a curative.

In a thirtieth aspect, the mixing step of the method in accordance withany one of the twenty-sixth to twenty-ninth aspects is performedbatch-wise or continuously.

In a thirty-first aspect, the mixing step of the method in accordancewith any one of the twenty-sixth to thirtieth aspects is performed bycontinuously feeding the base elastomer composition and at least aportion of the composite particles into an initial portion of a mixingpath to produce a blend, and then continuously feeding the blend into asecond portion of the mixing path.

The following examples are intended to illustrate certain aspects of thepresent invention and are not intended to limit the scope of theinvention.

Example 1

A waterborne graphene dispersion was prepared with the components listedin Table 1.

TABLE 1 Component Wt. % Deionized Water 89.3 Polyvinylpyrrolidone(PVP10)⁽¹⁾  2.7 Pure Wave ™ Graphene Nanoplatelets⁽²⁾  8 ⁽¹⁾From SigmaAldrich with a reported average molecular weight 10,000 g/mol.

(²) Commercially Available from Raymor NanoIntegris

The PVP was added to the water while mixing with a Cowles blade untilfully dissolved. The Graphene Nanoplatelets material was gradually addedwhile aggressively stirring with a Cowles blade, starting at 500 RPM andsteadily increasing up to 2000 RPM as needed to form a pre-dispersedmaterial, which was then milled using an Eiger mill with ceramic micromilling beads 1-1.2 mm in size to a residence time of 20 minutes todecrease the particle size to less than 1 m.

Example 2

A silica dispersion was prepared with the components listed in Table 2.

TABLE 2 Waterborne Hi-Sil EZ160 Silica Solution Component Wt. % DI Water84 Hi-Sil ™ EZ160⁽³⁾ 16 ⁽³⁾Precipitated silica commercially availablefrom PPG Industries.

Approximately 1.5 kg of powdered silica was charged to a five-gallonbucket and 7.9 kg of water was added to reach the 16% solids content asgiven in Table 2. The silica and water mixture were then sheared for 5minutes at approximately 8,000 RPM using a Premier Mill 2500 HVlaboratory disperser fitted with a 3-inch diameter Norstone type 7HHSpolyethylene Polyblade with three scoops and three teeth and a 2.0horsepower motor. The solution was then again stirred with a high liftblade for one hour immediately before using.

Example 3

Mixed dispersions containing differing amounts of graphene were madeaccording to Table 3.

TABLE 3 Combined Waterborne Silica and Graphene Dispersions SampleSample Sample Components A B C Graphene dispersion of Example 1  50 g 25 g  10 g Silica dispersion of Example 2 175 g 190 g 195 g DI water175 g 190 g 195 g % graphene (vs. total graphene/silica) 12.5% 6.25%2.5%

The graphene dispersion of Example 1 was added to the silica dispersionof Example 2 at three different graphene to silica ratios. The fillerpercentage of graphene reported in Table 3 is relative to the totalfiller, graphene and silica.

The dispersions of Samples A, B, and C were evaluated with a Mastersizer2000 particle size analyzer, purchased from Malvern Panalytical Ltd. Theindividual particle sizes of the graphene and silica are reported belowin Table 4.

TABLE 4 Particle Sizes of graphene and silica in dispersionMastersizer - Mastersizer - Sample Graphene (μm) Silica (μm) A 38.1437.17 B 22.99 20.69 C 40.71 39.60

Example 4

Sample A, Sample B, and Sample C from Table 3 were spray dried using aBuchi Spray Dryer, commercially available from Buchi Corporation with a0.5 mm nozzle. Table 5 shows the conditions used to prepare the spraydried Samples D, E and F. SLPH means standard liter per hour. FIG. 1 isan SEM micrograph of a silicon-graphenic carbon composite particleproduced by spray drying of Sample E at 10,000× magnification. FIG. 2 isan SEM micrograph of the same composite particle at 100,000×magnification. Non-spherical graphene platelets are visible at themagnification of FIG. 2 .

TABLE 5 Spray Dry Parameters with 0.5 mm Nozzle Atomizer Inlet OutletNozzle Nozzle Flow Aspirator Temperature Temperature Cleaner CoolingSample Dispersion (SLPH) % (° C.) (° C.) (on/off) (on/off) D Sample A600 60 220 90 On On E Sample B 600 60 220 90 On Or F Sample C 600 60 22090 On On

The particle sizes of the spray dried composite materials were measuredusing FE-SEM micrographs. Three images were captured at the samemagnification in three different areas on the sample. The diameter of 10particles in each area were measured at random for a total of 30measured particles. The measurements were then averaged to obtain anaverage particle size and range of composite particle sizes. Theparticle size distribution of the composite particles is listed in Table6.

TABLE 6 Particle Sizes of composite particles Spray Dried CompositeParticle Sample Size (μm) D 5.25 +/− 2 E 5.25 +/− 2 F 4.42 +/− 1

Example 5

A waterborne silica and graphene oxide dispersion was prepared with thecomponents listed in Table 7.

TABLE 7 Waterborne Hi-Sil EZ160 Silica - Graphene Oxide SolutionComponents Sample G Graphene Oxide 2.5% dispersion⁽¹⁾ 400 g Hi-Sil ™EZ160⁽²⁾ 150 g DI water 600 g % graphene oxide (vs. total graphene 6.25%oxide/silica) ⁽¹⁾Commercially available from Graphenea, Inc.⁽²⁾Precipitated silica commercially available from PPG Industries.

The Graphene Oxide was purchased from Graphenea Inc. as a 2.5 wt %dispersion of graphene oxide in water. The graphene oxide dispersion wasfurther diluted with the amount of DI water indicated in Table 7. Thedispersion was placed in a 2-liter beaker and stirred with an overheadstirrer fitted with a polyethylene blade. Slowly, 150 g of silica fromTable 7 was added to the mixture. A homogeneous dispersion with thecomposition of Table 7 was obtained. Because the 400 g of graphene oxidefrom Graphenea, Inc. contains 2.5% of graphene oxide, the total amountof graphene oxide in the dispersion is 10 g. Since 150 g of silica wereadded, the resulting graphene oxide concentration in the silica-grapheneoxide composite would be 6.25 wt %. The final dispersion was driedaccording to Example 4 with the conditions listed in Table 5 to obtain adried composite.

Example 6

A rubber compound was prepared using the model passenger treadformulation listed in Table 8. For this example, the silica fillertraditionally used in rubber compounds was replaced by thesilica-graphene composite of the invention. The silica-graphenecomposite used in this example consists of Sample E from Table 5. SinceSample E has a 6.25% of graphene, it can also be said that the 80 partsof composite filler in the compound is composed of 75 parts of silicaand 5 parts of graphene.

TABLE 8 Example 6 Rubber Formulation Component Parts (phr) Charge 1 JSRHPR 350R⁽⁴⁾  75 Budene ® 1207⁽⁵⁾  25 Charge 2 Composite Sample E  80Vivatec ® 500 US⁽⁶⁾  28.33 Si 266 ®⁽⁷⁾  6.4 ZnO  2.5 Stearic acid  2.0Santoflex ® 13⁽⁸⁾  1.5 Charge 3 RM Sulfur⁽⁹⁾  1.8 CBS⁽¹⁰⁾  1.7 DPG⁽¹¹⁾ 2.0 Total phr: 226.23 ⁽⁴⁾Solution styrene-butadiene rubber (SSBR);vinyl content: 58%, styrene content: 27%, Mooney viscosity (ML(1 +4)100° C.): 65; obtained commercially from JSR. ⁽⁵⁾Butadiene rubber(BR); cis 1,4 content 97%, Mooney viscosity (ML(1 + 4)100° C.): 55;obtained commercially from The Goodyear Tire & Rubber Co. ⁽⁶⁾Aprocessing oil obtained commercially from Hansen & Rosental.⁽⁷⁾3,3′-bis(triethoxy-silylpropyl)disulfide obtained commercially fromMomentive. ⁽⁸⁾N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamineantiozonant, obtained commercially from Flexsys. ⁽⁹⁾Rubber Makers (RM)Sulfur, 100% active, obtained commercially from Taber, Inc.⁽¹⁰⁾N-cyclohexyl-2-benzothiazolesulfenamide obtained commercially fromFlexsys. ⁽¹¹⁾Diphenylguanidine, obtained commercially from Monsanto.

The compound was mixed in a C. W. Brabender® Intelli-TorquePlasti-Corder Torque Rheometer equipped with a 350 mL mixer head fittedwith Banbury blades and using a fill factor of 75%.

The formulation was mixed using two non-productive passes, allowing thecompound to cool between passes, followed by a productive pass where thecuratives were added. For the first pass, the mixer rotors speed was setto 60 RMP and the components of Charge 1 were added to the mixer duringthe first 60 seconds of mixing. After 60 seconds into the mix cycle, thecomponents of Charge 2 were added in the mixer. The first pass wasdropped at four minutes from the starting of the mixing, at which pointthe mixing temperature had reached about 160° C.

For the second pass, the mixer rotors speed was kept at 60 RPM, and thecooled first pass Masterbatch was added during the first minute ofmixing, slowly to avoid stalling the mixer. The second pass was droppedat four minutes when a drop temperature of about 160° C. was reached.

For the final pass, the mixer speed was kept at 40 RPM, and the cooledsecond pass Masterbatch was added during the first minute of mixing,slowly to avoid stalling the mixer. After adding the Masterbatch, Charge3 was added. The second pass was dropped at three minutes when a droptemperature of about 100° C. had been reached.

The resulting rubber composition was cured at 150° C. for a timesufficient to reach 90% of the maximum torque obtained using theoscillating Disk Rheometer (90% ODR) plus 5 minutes (T₉₀+5 minutes).

Example 7

A silica and graphene-oxide-containing rubber compound was preparedaccording to the procedure of Example 6, but replacing the compositeSample E with composite Sample G. Since Sample G has a 6.25% of grapheneoxide, it can also be said that the 80 parts of composite filler in thecompound is composed of 75 parts of silica and 5 parts of grapheneoxide. Comparative Example 1 (CE-1)

A silica and graphene-containing rubber compound was prepared accordingto the procedure of Example 6 but replacing the composite Sample E with75 parts free Hi-Sil EZ 160G and 5 parts free PureWave™ GrapheneNanoplatelets (predispersed in the Vivatec® 500 us, for purposes of safehandling).

Comparative Example 2 (CE-2)

A rubber compound was prepared according to the procedure of Example 6but replacing the composite Sample E with 80 parts free Hi-Sil EZ 160G.No graphene was added, resulting in a graphene-free rubber representinga standard silica-filled rubber composition.

Results

The resulting vulcanizates of Example 6 and Comparative Examples 1 and 2were tested for various physical properties in accordance with standardASTM procedures.

As seen in Table 9, cure level (as indicated by S′ max, S′ min and T50values) and hardness for all compounds are similar, enabling comparisonsof the remaining data.

TABLE 9 Compound Performance Data Example 6 Silica- CE-1 CE-2 Graphene75 parts silica: 80 parts Filler Composite 5 parts graphene silica S′Max, dNm  20.5  18.8  20.2 S′ Min, dNm  6.9  6.4  9.0 T50, min  23.7 24.4  24.6 Tensile, MPa  8.3  4.1  2.6 Elongation, % 588 580 331Modulus @ 100%, MPa  1.3  0.9  1.1 Modulus @ 300%, MPa  4.0  2.1  2.5300/100% Modulus ratio  3.2  2.2  2.4 Hardness @ 23° C.  63  60  65Hardness @ 100° C.  54  50  56 Rebound @ 23° C., %  40  41  45 Rebound @100° C., %  53  48  53 G′ @ 60° C., MPa  2.56  2.17  2.41 Tan (δ) @ 60°C.  0.184  0.200  0.174 Tan (δ) @ 0° C.  0.248  0.264  0.237 G′ @ 1.0%,30° C., MPa  4.08  3.12  3.75 DIN Abrasion index 108 92 100 Die C Tearstrength (N/mm)  50  57  37

It can be seen in Table 9 that CE-1 (5 phr of free graphene) has highertensile strength, elongation and tear strength than the compound withoutgraphene (CE-2). Significant benefits are obtained when thesilica-graphenic carbon composite is used (Example 6) as in thisinvention compared to adding the graphene directly in the mixer (CE-1).The composite-containing Example 6 shows a much higher reinforcementevidenced in several parameters such as more than doubled tensilestrength, 50% higher 300% o/100% modulus ratio, higher dynamic modulus(G′) and 17% higher abrasion resistance as compared to rubber where thegraphene and silica were added separately (CE-1). Significantimprovements are also demonstrated when compared to a standardsilica-filled rubber formulation (CE-2).

The resulting vulcanizate of Example 7 was also tested for variousphysical properties in accordance with standard ASTM procedure.

As seen in Table 10, hardness and dynamic stiffness (G′) is comparablefor the graphene oxide composite (Example 7) and silica compound (CE-2).

TABLE 10 Compound Performance Data Example 7 Silica- Graphene CE-2 Oxide80 parts Filler Composite silica S′ Max, dNm  29.1  20.2 S′ Min, dNm 5.3  9.0 T50, min  17.4  24.6 Tensile, MPa  17.7  2.6 Elongation, % 505331 Modulus @ 100%, MPa  2.6  1.1 Modulus @ 300%, MPa  9.6  2.5 300/100%Modulus ratio  3.7  2.4 Hardness @ 23° C.  65  65 Hardness @ 100° C.  63 56 Rebound @ 23° C., %  50  45 Rebound @ 100° C., %  66  53 G′ @ 60°C., MPa  2.45  2.41 Tan (δ) @ 60° C.  0.108  0.174 Tan (δ) @ 0° C. 0.198  0.237 G′ @ 1.0%, 30° C., MPa  3.06  3.75 DIN Abrasion index 110100 Die C Tear strength (N/mm)  45  37

Significant benefits are obtained when the silica-graphene oxidecomposite is used (Example 7) as in this invention compared to thesilica control compound (CE-2). The composite-containing Example 7 showsa much higher reinforcement evidenced in several parameters such ashigher tensile strength, higher elongation and higher 300%/100% modulusratio. Also, improvements in hysteresis (Tan (6) @ 60° C.), DIN abrasionresistance and tear strength are demonstrated.

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

We claim:
 1. Silica-graphenic carbon composite particles comprising from60 to 99.9 weight percent silica and from 0.1 to 40 weight percentgraphenic carbon, wherein the graphenic carbon is distributed throughouteach composite particle, and the silica comprises multiple silicaparticles contacting each other in a continuous or interconnectednetwork in which the graphenic carbon is distributed.
 2. Thesilica-graphenic carbon composite particles of claim 1, wherein thecomposite particles have an average particle size of from 2 to 100microns.
 3. The silica-graphenic carbon composite particles of claim 1,wherein the graphenic carbon is selected from graphite oxide, grapheneoxide, rGO, or combinations thereof.
 4. A method of makingsilica-graphenic carbon composite particles, the method comprisingdrying a slurry comprising silica particles, graphenic carbon particlesand a liquid carrier to thereby produce the silica-graphenic carboncomposite particles, wherein the graphenic carbon is dispersedthroughout each silica-graphenic carbon composite particle, and thesilica comprises a continuous or interconnected network in which thegraphenic carbon is dispersed.
 5. The method of claim 4, wherein thedrying comprises spray drying.
 6. The method of claim 4, wherein theliquid carrier comprises water.
 7. The method of claim 4, wherein theslurry further comprises a dispersing agent.
 8. An elastomericformulation comprising: a base elastomer composition; and from 5 to 70weight percent silica-graphenic carbon composite particles comprisingfrom 60 to 99.9 weight percent silica and from 0.1 to 40 weight percentgraphenic carbon, wherein the graphenic carbon is distributed throughouteach silica-graphenic carbon composite particle, and the silicacomprises a continuous or interconnected network in which the grapheniccarbon is distributed.
 9. The elastomeric formulation of claim 8,wherein the base elastomer composition comprises natural rubber,synthetic rubber, or combinations thereof.
 10. The elastomericformulation of claim 8, wherein the base elastomer composition comprisesstyrene/butadiene rubber, butadiene rubber, butyl rubber, EPDM rubber,nitrile rubber, chloroprene rubber, silicone rubber, fluoroelastomerrubber, natural rubber, and/or functionalized derivatives thereof. 11.The elastomeric formulation of claim 8, wherein the elastomericformulation is a tire tread formulation.
 12. The elastomeric formulationof claim 8, wherein the elastomer composition comprises at least oneadditive selected from processing oils, antioxidants, curatives, ormetal oxides.
 13. The elastomeric formulation of claim 8, wherein thecomposite particles are present in the formulation in an amount of from30 to 50 weight percent of the formulation.
 14. A method of making anelastomeric formulation comprising: mixing silica-graphenic carboncomposite particles with a base elastomer composition; and curing themixture, wherein the graphenic carbon is distributed throughout eachsilica-graphenic carbon composite particle, and the silica comprises acontinuous or interconnected network in which the graphenic carbon isdistributed.
 15. The method of claim 14, wherein the base elastomercomposition comprises natural rubber, synthetic rubber, or combinationsthereof.
 16. The method of claim 14, wherein the base elastomercomposition comprises styrene/butadiene rubber, butadiene rubber, butylrubber, EPDM rubber, nitrile rubber, chloroprene rubber, siliconerubber, fluoroelastomer rubber, natural rubber, and/or functionalizedderivatives thereof.
 17. The method of claim 14, wherein the elastomericformulation is a tire tread formulation.
 18. The method of claim 14,wherein the elastomer composition comprises at least one additiveselected from processing oils, antioxidants, curatives, or metal oxides.19. The method of claim 14, wherein the composite particles are presentin the formulation in an amount of from 30 to 50 weight percent of theformulation.